The invention relates to a process for the finishing of ball-and-socket joints destined for constant-velocity joints which are provided with inner and outer bearing surfaces and ball pockets for the accommodation of torque-transmitting balls.
In motor vehicles with front wheel drive the steered wheels are driven. For that reason front wheel axle shafts must have joints which permit both the spring deflection and rebound of the wheels as well as their steering deflection. In order to allow the most uniform possible drive of the wheels constant-velocity joints are used. In doing so homocinetic fixed joints constructed inter alia as cup-type joints are used for joints on front axle shafts while homocinetic displacement joints, which in addition to bending of the joint allow an axial displacement, also constructed as cup-type joints are used for joints on rear axle shafts.
These cup-type joints consist of a ball star placed on the axle shaft end on the wheel side on which the ball cage with balls and the ball cup connected to the wheel drive shaft are seated. In the case of the homocinetic fixed joint the ball cup and ball star have curved races on which the balls move. In the case of the homocinetic displacement joint the path of motion on the ball cup and ball star are of flat construction.
In the constant-velocity joints known in practice consisting of ball star, ball cage and ball cup, the ball cages provided with spherical inner and outer bearing surfaces and ball pockets for the accommodation of the torque-transmitting balls are first of all produced as blanks in a large number of forging, stamping and turning steps on various machines. Starting from these blanks the finishing of the ball cages ensues once again in a large number of work steps on various machines, the machine-cutting methods used being in particular grinding processes for machining the bearing surfaces and for machining the contact surfaces of the balls in the ball pockets. It is disadvantageous in this known finishing process that the final machining of each ball cage comprises several different working steps which have to be carried out on different machines. On account of the large number of working steps on different machines which cannot be carried out continuously in automatic manner the final machining of the ball cages is time-consuming and costly. Moreover, on account of the different clamping sizes errors occur so that tolerances are possible only within certain limits.
The underlying aim of the invention is to provide a method for the machine finishing of ball cages destined for constant-velocity joints which allows simple, low-cost and fully automated finishing of the ball cages which moreover ensues with increased precision.
The solution to this task is characterised according to the invention in that the production of both the inner and outer spherical annular bearing surfaces as well as the contact surfaces of the ball pockets located opposite one another in the axial direction and each for one ball ensues by means of lathe machining.
Due to the reduction according to the invention of the working steps necessary for machine finishing to lathe machining it is possible to carry out the finishing of ball cages rapidly, at low cost, with full automation and with increased precision. Due to the fact that the finishing of the ball cages by the method according to the invention requires only further lathe machining tasks on the blanks it is possible for all lathe machining tasks on a ball cage to ensue on the same lathe. By comparison with the known finishing operation in various working steps on different machines the finishing process according to the invention exhibits clear time, cost and precision advantages.
According to a practical embodiment of the invention it is proposed that first of all the inner spherical annular bearing surfaces, a contact surface on the end face and two annular, cylindrical clamping surfaces bounding the inner bearing surface are turned in one clamping step and that the ball cage machined in this way is rechucked by means of the cylindrical clamping surfaces and the contact surface on the end face. In order to permit continuous machining with rechucking of the workpiece only once, apart from the machine finishing of the inner spherical annular bearing surface in the first work step in an initial chucking of the workpiece there ensues the construction of various clamping surfaces which are needed so that in a succeeding chucking step the remaining surfaces can be machined in one lathe machining operation.
It is furthermore proposed according to the invention that after rechucking has taken place the outer spherical annular bearing surface and the contact surfaces constructed in the ball pockets each for one ball are machined by turning. Due to the rechucking of the partly machined ball cage which can ensue in fully automatic manner on the same lathe it is possible without any delay to do the machine finishing of the remaining surfaces in a further turning process. Thus overall it is evident that the entire finishing of a ball cage can ensue by means of lathe machining on the same lathe, it only being necessary for the machining of the different surfaces to construct in a first working step chucking surfaces which are necessary for holding the workpiece in the second turning step. Since on the one hand only lathe machining processes are used and on the other hand these can be carried out on the same machine it is possible to carry out the finishing according to the invention in fully automatic manner and hence rapidly and at low cost.
According to a preferred specific embodiment of the invention the machining of the two contact surfaces located opposite one another ensues simultaneously, i.e. during each insertion of the lathe tool into a ball pocket.
Finally, it is proposed according to a practical embodiment of the invention that the two contact surfaces located opposite one another are machined one after the other by feeding the lathe tool in the axial direction of the spindle axis of the workpiece. The turning method can be a hard turning method so that hardened workpieces can also be machined.